1. Field of the Invention
This invention relates to a supporting plate, a stage device, an exposure device, and an exposure method, and particularly to a supporting plate which is advantageously used with respect to a substrate on a stage, a stage device, an exposure apparatus, and an exposure method, at the time of exposure via a projection optical system that utilizes a liquid immersion technique.
2. Description of Related Art
A semiconductor device and a liquid crystal display device are manufactured by a so-called photolithographic method which transfers a pattern formed on a mask onto a photosensitive substrate. An exposure apparatus which is used in this photolithographic method is provided with a mask stage which supports a mask, and a substrate stage which supports a substrate. The exposure apparatus transfers a mask pattern onto a substrate via a projection optical system while successively moving the mask stage and the substrate stage. Recently, higher resolution of the projection optical system corresponding to higher integration of a device pattern is demanded. The resolution of the projection optical system increases as an exposure wavelength which is used becomes shorter and a numerical aperture of the projection optical system becomes larger. Because of this, the exposure wavelength which is used in exposure apparatus has become shortened over the years, and the numerical aperture of projection optical systems has increased. Furthermore, an exposure wavelength of 248 nm of a KrF excimer laser is currently the mainstream, but an exposure wavelength of 139 nm of an ArF excimer laser also has been put into practice. In addition, in the case of performing exposure, a depth of focus (DOF) also becomes important as well as the resolution. The resolution R and the depth of focus δ can be expressed by the following equations.R=k1·λ/NA  (1)δ=±k2·λ/NA2  (2)
Here, λ is an exposure wavelength, NA is a numerical aperture of the projection optical system, and k1, k2 are process coefficients. According to equations (1) and (2), in order to increase the resolution R, by shortening the exposure wavelength λ and increasing the numerical aperture NA, it is understood that the depth of focus δ becomes narrower.
When the depth of focus δ becomes too narrow, it is difficult to match a substrate surface with an image plane of the projection optical system, and there is a possibility that a focus margin may become insufficient at the time of an exposure operation. Therefore, a liquid immersion method has been proposed, as disclosed in, e.g., WO99/49504, as a method which substantially shortens an exposure wavelength and broadens the depth of focus. This liquid immersion method forms a liquid immersion area by filling the space between a lower surface of the projection optical system and a substrate surface with liquid such as water, an organic solvent, or the like, and improves the resolution by taking advantage of the fact that the wavelength of the exposure light in liquid becomes 1/n (n is normally approximately 1.2 through 1.6 depending on the index of refraction of the liquid) as compared to the wavelength in air, and increases the depth of focus by approximately n-times.